Nonsingular black hole models

Last updated

A nonsingular black hole model is a mathematical theory of black holes that avoids certain theoretical problems with the standard black hole model, including information loss and the unobservable nature of the black hole event horizon.

Contents

Avoiding paradoxes in the standard black hole model

For a black hole to physically exist as a solution to Einstein's equation, it must form an event horizon in finite time relative to outside observers. This requires an accurate theory of black hole formation, of which several have been proposed. In 2007, Shuan Nan Zhang of Tsinghua University proposed a model in which the event horizon of a potential black hole only forms (or expands) after an object falls into the existing horizon, or after the horizon has exceeded the critical density. In other words, an infalling object causes the horizon of a black hole to expand, which only occurs after the object has fallen into the hole, allowing an observable horizon in finite time. [1] [2] This solution does not solve the information paradox, however.

Alternative black hole models

Nonsingular black hole models have been proposed since theoretical problems with black holes were first realized.[ citation needed ] Today some of the most viable candidates for the result of the collapse of a star with mass well above the Chandrasekhar limit include the gravastar and the dark energy star.

While black holes were a well-established part of mainstream physics for most of the end of the 20th century, alternative models received new attention when models proposed by George Chapline and later by Lawrence Krauss, Dejan Stojkovic, and Tanmay Vachaspati of Case Western Reserve University showed in several separate models that black hole horizons could not form. [3] [4]

Such research has attracted much media attention, [5] as black holes have long captured the imagination of both scientists and the public for both their innate simplicity and mysteriousness. The recent theoretical results have therefore undergone much scrutiny and most of them are now ruled out by theoretical studies. For example, several alternative black hole models were shown to be unstable in extremely fast rotation, [6] which, by conservation of angular momentum, would be a not unusual physical scenario for a collapsed star (see pulsar). Nevertheless, the existence of a stable model of a nonsingular black hole is still an open question.

Hayward metric

The Hayward metric is the simplest description of a black hole that is non-singular. The metric was written down by Sean Hayward as the minimal model that is regular, static, spherically symmetric and asymptotically flat. [7]

Ayón-Beato–García metric

The Ayón-Beato–García model is the first exact charged regular black hole with a source. [8] The model was proposed by Eloy Ayón Beato and Alberto García in 1998 based on the minimal coupling between a nonlinear electrodynamics model and general relativity, considering a static and spherically symmetric spacetime. Later the same authors reinterpreted the first non-singular black hole geometry, the Bardeen toy Model, [9] as a nonlinear-electrodynamics-based regular black hole. [10] Nowadays, it is known that the Ayón-Beato–García model may mimic the absorption properties of the Reissner–Nordström metric, from the perspective of the absorption of massless test scalar fields. [11]

Nonsingular black holes as dark matter

In 2024, Paul C.W. Davies, Damien A. Easson, and Phillip B. Levin proposed that nonsingular black holes are a viable candidate for dark matter [12] . They showed that the nonsingular Schwarzschild-de Sitter black hole slowly evaporates, reaching a maximum but finite temperature, then forms a black hole remnant that does not have a singularity and whose mass is on the order of the Planck mass. This nonsingular black hole can comprise all of the dark matter in the observable universe because the fraction of primordial black holes that is dark matter is inversely proportional to the smallest mass primordial black hole that could have survived since the primordial era. It was previously thought that Hawking evaporation set the lower bound of primordial black holes to be 1012 kg, but nonsingular black holes, which form remnants and do not evaporate completely, lower this bound to the Planck mass, which is 10-8 kg. Thus Planck mass nonsingular black holes formed primordially can comprise all of the dark matter in the observable universe today.

See also

Related Research Articles

<span class="mw-page-title-main">Black hole</span> Object that has a no-return boundary

A black hole is a region of spacetime wherein gravity is so strong that no matter or electromagnetic energy can escape it. Albert Einstein's theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole. The boundary of no escape is called the event horizon. A black hole has a great effect on the fate and circumstances of an object crossing it, but it has no locally detectable features according to general relativity. In many ways, a black hole acts like an ideal black body, as it reflects no light. Quantum field theory in curved spacetime predicts that event horizons emit Hawking radiation, with the same spectrum as a black body of a temperature inversely proportional to its mass. This temperature is of the order of billionths of a kelvin for stellar black holes, making it essentially impossible to observe directly.

<span class="mw-page-title-main">Cosmic inflation</span> Theory of rapid universe expansion

In physical cosmology, cosmic inflation, cosmological inflation, or just inflation, is a theory of exponential expansion of space in the very early universe. Following the inflationary period, the universe continued to expand, but at a slower rate. The re-acceleration of this slowing expansion due to dark energy began after the universe was already over 7.7 billion years old.

In general relativity, a naked singularity is a hypothetical gravitational singularity without an event horizon.

<span class="mw-page-title-main">Wormhole</span> Hypothetical topological feature of spacetime

A wormhole is a hypothetical structure connecting disparate points in spacetime. It can be visualized as a tunnel with two ends at separate points in spacetime. Wormholes are based on a special solution of the Einstein field equations. Specifically, they are a transcendental bijection of the spacetime continuum, an asymptotic projection of the Calabi–Yau manifold manifesting itself in anti-de Sitter space.

<span class="mw-page-title-main">Timeline of gravitational physics and relativity</span>

The following is a timeline of gravitational physics and general relativity.

Hawking radiation is the theoretical emission released outside a black hole's event horizon. This is counterintuitive because once ordinary electromagnetic radiation is inside the event horizon, it cannot escape. It is named after the physicist Stephen Hawking, who developed a theoretical argument for its existence in 1974. Hawking radiation is predicted to be extremely faint and is many orders of magnitude below the current best telescopes' detecting ability.

An axion is a hypothetical elementary particle originally theorized in 1978 independently by Frank Wilczek and Steven Weinberg as the Goldstone boson of Peccei–Quinn theory, which had been proposed in 1977 to solve the strong CP problem in quantum chromodynamics (QCD). If axions exist and have low mass within a specific range, they are of interest as a possible component of cold dark matter.

<span class="mw-page-title-main">Big Bounce</span> Model for the origin of the universe

The Big Bounce hypothesis is a cosmological model for the origin of the known universe. It was originally suggested as a phase of the cyclic model or oscillatory universe interpretation of the Big Bang, where the first cosmological event was the result of the collapse of a previous universe. It receded from serious consideration in the early 1980s after inflation theory emerged as a solution to the horizon problem, which had arisen from advances in observations revealing the large-scale structure of the universe.

A gravastar is an object hypothesized in astrophysics by Pawel O. Mazur and Emil Mottola as an alternative to the black hole theory. It has usual black hole metric outside of the horizon, but de Sitter metric inside. On the horizon there is a thin shell of matter. The term "gravastar" is a portmanteau of the words "gravitational vacuum star". Further theoretical considerations of gravastars include the notion of a nestar.

The Immirzi parameter is a numerical coefficient appearing in loop quantum gravity (LQG), a nonperturbative theory of quantum gravity. The Immirzi parameter measures the size of the quantum of area in Planck units. As a result, its value is currently fixed by matching the semiclassical black hole entropy, as calculated by Stephen Hawking, and the counting of microstates in loop quantum gravity.

Micro black holes, also called mini black holes or quantum mechanical black holes, are hypothetical tiny black holes, for which quantum mechanical effects play an important role. The concept that black holes may exist that are smaller than stellar mass was introduced in 1971 by Stephen Hawking.

In black hole physics and inflationary cosmology, the trans-Planckian problem is the problem of the appearance of quantities beyond the Planck scale, which raise doubts on the physical validity of some results in these two areas, since one expects the physical laws to suffer radical modifications beyond the Planck scale.

Numerical relativity is one of the branches of general relativity that uses numerical methods and algorithms to solve and analyze problems. To this end, supercomputers are often employed to study black holes, gravitational waves, neutron stars and many other phenomena described by Albert Einstein's theory of general relativity. A currently active field of research in numerical relativity is the simulation of relativistic binaries and their associated gravitational waves.

An exotic star is a hypothetical compact star composed of exotic matter, and balanced against gravitational collapse by degeneracy pressure or other quantum properties.

<span class="mw-page-title-main">Primordial black hole</span> Hypothetical black hole formed soon after the Big Bang

In cosmology, primordial black holes (PBHs) are hypothetical black holes that formed soon after the Big Bang. In the inflationary era and early radiation-dominated universe, extremely dense pockets of subatomic matter may have been tightly packed to the point of gravitational collapse, creating primordial black holes without the supernova compression typically needed to make black holes today. Because the creation of primordial black holes would pre-date the first stars, they are not limited to the narrow mass range of stellar black holes.

A black star is a gravitational object composed of matter. It is a theoretical alternative to the black hole concept from general relativity. The theoretical construct was created through the use of semiclassical gravity theory. A similar structure should also exist for the Einstein–Maxwell–Dirac equations system, which is the (super) classical limit of quantum electrodynamics, and for the Einstein–Yang–Mills–Dirac system, which is the (super) classical limit of the standard model.

The asymptotic safety approach to quantum gravity provides a nonperturbative notion of renormalization in order to find a consistent and predictive quantum field theory of the gravitational interaction and spacetime geometry. It is based upon a nontrivial fixed point of the corresponding renormalization group (RG) flow such that the running coupling constants approach this fixed point in the ultraviolet (UV) limit. This suffices to avoid divergences in physical observables. Moreover, it has predictive power: Generically an arbitrary starting configuration of coupling constants given at some RG scale does not run into the fixed point for increasing scale, but a subset of configurations might have the desired UV properties. For this reason it is possible that — assuming a particular set of couplings has been measured in an experiment — the requirement of asymptotic safety fixes all remaining couplings in such a way that the UV fixed point is approached.

The Hayward metric is the simplest description of a black hole which is non-singular. The metric was written down by Sean Hayward as the minimal model which is regular, static, spherically symmetric and asymptotically flat. The metric is not derived from any particular alternative theory of gravity, but provides a framework to test the formation and evaporation of non-singular black holes both within general relativity and beyond. Hayward first published his metric in 2005 and numerous papers have studied it since.

Katelin Schutz is an American particle physicist known for using cosmological observations to study dark sectors, that is new particles and forces that interact weakly with the visible world. She was a NASA Einstein Fellow and Pappalardo Fellow in the MIT Department of Physics and is currently an assistant professor of physics at McGill University.

Direct detection of dark matter is the science of attempting to directly measure dark matter collisions in Earth-based experiments. Modern astrophysical measurements, such as from the Cosmic Microwave Background, strongly indicate that 85% of the matter content of the universe is unaccounted for. Although the existence of dark matter is widely believed, what form it takes or its precise properties has never been determined. There are three main avenues of research to detect dark matter: attempts to make dark matter in accelerators, indirect detection of dark matter annihilation, and direct detection of dark matter in terrestrial labs. The founding principle of direct dark matter detection is that since dark matter is known to exist in the local universe, as the Earth, Solar System, and the Milky Way Galaxy carve out a path through the universe they must intercept dark matter, regardless of what form it takes.

References

  1. ↑ Zhang, Shuang Nan; Tang, Sumin (2007-07-06). "Witnessing matter falling into a black hole by a distant observer". Tsinghua University. Retrieved 2007-11-03.[ permanent dead link ]
  2. ↑ Zhang, Shuang Nan; Liu, Yuan (2008). "Observe matter falling into a black hole". AIP Conf. Proc. 968: 384–391. arXiv: 0710.2443 . Bibcode:2008AIPC..968..384Z. doi:10.1063/1.2840436. S2CID   15169576.
  3. ↑ Chapline, George (July 1998). "The Black Hole Information Puzzle and Evidence for a Cosmological Constant". arXiv: hep-th/9807175 .
  4. ↑ Vachaspati, Tanmay; Dejan Stojkovic; Lawrence M. Krauss (June 2007). "Observation of Incipient Black Holes and the Information Loss Problem". Phys. Rev. D. 76 (2): 024005. arXiv: gr-qc/0609024 . Bibcode:2007PhRvD..76b4005V. doi:10.1103/PhysRevD.76.024005. S2CID   119333620.
  5. ↑ Rockets, Rusty (2007-06-22). "Rethinking Black Holes". Science A Gogo. Retrieved 2007-11-03.
  6. ↑ Cardoso, Vitor; Paolo Pani; Mariano Cadoni; Marco Cavaglia (2008). "Ergoregion instability rules out black hole doubles". Phys. Rev. D. 77 (12): 124044. arXiv: 0709.0532 . Bibcode:2008PhRvD..77l4044C. doi:10.1103/PhysRevD.77.124044. S2CID   119119838.
  7. ↑ Hayward, Sean A. (26 January 2006). "Formation and evaporation of non-singular black holes". Physical Review Letters . 96 (3): 031103. arXiv: gr-qc/0506126 . Bibcode:2006PhRvL..96c1103H. doi:10.1103/PhysRevLett.96.031103. PMID   16486679. S2CID   15851759.
  8. ↑ Ayón-Beato, Eloy; García, Alberto (8 June 1998). "Regular Black Hole in General Relativity Coupled to Nonlinear Electrodynamics". Physical Review Letters . 80 (23): 5056–5059. arXiv: gr-qc/9911046 . Bibcode:1998PhRvL..80.5056A. doi:10.1103/PhysRevLett.80.5056. PMID   16486679. S2CID   39766986.
  9. ↑ Bardeen, JM (1968). "Non-singular general relativistic gravitational collapse". In Proceedings of the International Conference GR5, Tbilisi, USSR. 174: 87. Bibcode:1968qtr..conf...87B.
  10. ↑ Ayón-Beato, Eloy; García, Alberto (9 November 2000). "The Bardeen model as a nonlinear magnetic monopole". Physical Review B . 493 (1–2): 149–152. arXiv: gr-qc/0009077 . Bibcode:2000PhLB..493..149A. doi:10.1016/S0370-2693(00)01125-4. S2CID   55773188.
  11. ↑ Paula, Marco; Leite, Luiz; Crispino, Luís (12 November 2020). "Electrically charged black holes in linear and nonlinear electrodynamics: Geodesic analysis and scalar absorption". Physical Review D . 102 (10): 104033. arXiv: 2011.08633 . Bibcode:2020PhRvD.102j4033P. doi:10.1103/PhysRevD.102.104033. PMID   16486679. S2CID   226975771.
  12. ↑ Davies, Paul C.W.; Easson, Damien A.; Levin, Phillip B. (28 October 2024). "Nonsingular black holes as dark matter". arXiv.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.